Daboub, et al. U.S. Pat. No. 5,109,987 May 5, 1992 describes a multilevel mail sorting machine of a type which is now in widespread use in various forms, with specific machines known as DBCS and MLOCR. For years, the United States Postal Service (USPS) has been sorting letter mail using automation equipment. The size of mail sorted on this equipment is limited to a specification listed in the Domestic Mail Manual (DMM) and generally meets the criteria listed below.
Each letter-size piece must be rectangular and:                a) For height, no more than 6⅛ or less than 3½ inches high.        b) For length, no more than 11½ or less than 5 inches long.        c) For thickness, no more than ¼ inch or less than                    (1) 0.007 inch thick if no more than 4¼ inches high and 6 inches long; or            (2) 0.009 inch thick if more than 4¼ inches high or 6 inches long, or both                        d) Weight not to exceed 3.3 ounces.The aspect ratio (length of the mail piece divided by height) must be between 1.3 and 2.5 inclusive.        
Recently the USPS has deployed equipment which is capable of sorting mail up to 0.5 inch thick and which can weigh up to 6.0 ounces. Mail which fits the increased standard is categorized as Expanded Capability (EC) mail and is sorted on a Delivery Bar Code Sorter Input/Output Sub-System (DIOSS EC) and DBCS EC machines manufactured by Siemens Postal Automation. Using the DIOSS EC machine, EC mail is sorted in a separate operation from the automation compatible mail.
At present, EC mail is only sorted to the Delivery Unit (DU) level. At the DU, the EC mail along with the residual manual mail is manually sorted to carrier route by a clerk, and then cased to delivery point sequence by a letter carrier. Compared to automation mail, manual mail, which includes EC mail in this example, is costly to sort. In contrast, automation compatible mail can be sorted to a finer sort depth, using multiple automated processes, to a Delivery Point Sequence (DPS) using efficient automation equipment, thus eliminating costly manual casing operations.
The original design of the DIOSS EC machines runs a smaller gap between the automation letters than the gap setting for EC letters. The gap setting is determined by the sort plan. If an automation sort plan is selected, the control computer downloads the gap setting to the feeder firmware. If an EC sort plan is selected, the control computer likewise downloads the gap setting to the feeder firmware, but for an EC sort plan, the control computer downloads a larger gap setting. Due to the geometry of the belt path, running a larger gap for EC mail is required if the leading mail piece is thick and the trailing mail piece is thin by comparison. Without the larger gap, the thin mail piece will not keep in pinch between the belts and rollers, causing slippage and/or jams. The result is that the machine throughput is significantly lower for EC mail than for automation mail due to the larger gap setting.
The USPS does not mix EC mail with automation mail during sorting because it wants automation mail to sort as fast as possible. It is undesirable to make 95% of the mail suffer the slower throughput penalty that is required for sorting EC mail. This invention provides a method for sorting mail previously classified as EC letters with the automation letters to a delivery point sequence in a manner that does not degrade the automation letter productivity.